In situ high-resolution measurement of phosphorus, iron and sulfur by diffusive gradients in thin films in sediments of black-odorous rivers in the Pearl River Delta region, South China.Environ Res. 2020 10; 189:109918.ER
The cycling of phosphorus (P), iron (Fe) and sulfur (S) in sediments has been previously investigated, but its impacts on the formation of black-odorous waterbodies remains unclear. Here, high-resolution (i.e., 2 mm for P and Fe, and 0.042 mm for S of 2D presentation) simultaneous measurements of P, Fe, and S profiles in river sediments based on the diffusive gradients in thin-films (DGT) technique were conducted in the Pearl River Delta region, South China. Similar distribution trends and significant positive correlations (R = 0.67-0.93, p < 0.01) were observed between Fe and P. Considering the high diffusion fluxes of Fe and P together, it revealed that P release was promoted by the Fe reduction. The two-dimensional labile S profiles showed that their concentrations in sediments were higher by factors of 1.6-20 than those in overlying water. The minor diffusion fluxes of S and the accumulation of acid volatile sulfide indicated that S2- combining with Fe2+ occurred prior to diffusion. Furthermore, the formation mechanisms of black-odorous waterbodies were explored: (i) oxygen depletion by COD and NH4+‒N and large amounts of sulfate input were the main exogenous driving factors. (ii) Reduction of Fe and S to form ferrous sulfide accompanied with P release in sediments were the dominant endogenous causes. These observations together with mechanism analysis can provide a basis for the governance of black-odorous rivers.